FRANCK RAMUS
vowels as /a/, liquids as /l/, plosives as /t/, nasals as /n/, and
glides as /j/ (20). Thus, each synthesized sentence preserved
only the prosodic characteristics of its natural counterpart,
while eliminating lexical and phonetic information.
Newborns were tested using the high amplitude suck-
ing procedure and a habituation/dishabituation design. Sen-
tences were elicited by the newborns’ sucking on a pacifier.
In the language change condition, newborns were habituated
to 10 sentences uttered by 2 speakers in one language and
then switched to 10 sentences uttered by 2 new speakers in
the other language. In the speaker change condition, new-
borns were habituated to 10 sentences uttered by 2 speakers
from one language and then switched to 2 new speakers in
the same language. A significant increase in sucking follow-
ing the language change, as compared to the speaker change,
is taken as evidence that newborns perceive a significant dif-
ference between the two languages (21).
Thirty-two newborns were tested (22) on the natural
language-forward experiment, 16 in the language change
condition and 16 in the speaker change condition. Figure
1A shows that the two groups did not differ significantly,
and thus that newborns failed to discriminate the two lan-
guages [F(1,29)<1] (23). This result appears to conflict with
previous experimental work showing that newborns discrim-
inate English and Japanese. However, our experiment ex-
poses newborns to great speaker variability (4 voices) (24),
and this factor has previously been shown to impair infants’
discrimination abilities (25). If speaker variability is respon-
sible for the absence of discrimination, then we would pre-
dict successful discrimination with fewer speakers. To test
for this possibility, we ran a second experiment using syn-
thesized speech, thereby reducing the number of voices to
one, that of the speech synthesizer (26).
Thirty-two additional newborns were tested (27) on the
forward language and speaker discrimination, using the syn-
thesized versions of the original sentences. Figure 1B shows
that newborns in the language change condition increased
their sucking significantly more during the 2 minutes follow-
ing the switch than newborns in the speaker change condi-
tion [F(1,29)=6.3, p=0.018]. This indicates that newborns
discriminate sentences of Dutch from sentences of Japanese,
relying exclusively on prosodic cues. Moreover, this result
shows that the newborns’ failure to discriminate in Experi-
ment 1A was probably due to speaker variability.
To determine the specificity of the newborns’ capacity to
discriminate languages, we tested 32 more newborns with the
same synthesized sentences, but played backwards (28). Fig-
ure 1C shows that newborns fail to discriminate languages
played backwards [F(1,29)<1] (29). Moreover, the interac-
tion between Experiments 1B and 1C (forward vs. back-
wards) is marginally significant [F(1,59)=3.6, p=0.06]. The
finding that newborns discriminate two non-native languages
played forward but not backwards suggests that the new-
borns’ language discrimination capacity may depend upon
specific properties of speech that are eliminated when the
signal is played backwards. However, before drawing such
a conclusion, it is important to directly assess the speech-
specificity of this capacity, by testing it on another species.
Figure 1. Average number of high amplitude sucks per minute for
babies in the control (speaker change, dotted lines) and in the exper-
imental group (speaker and language change, solid lines). Minutes
are numbered from the time of change, marked with a vertical line.
Error bars represent +/-1 standard error of the mean. 1A: natural
sentences played forward. 1B: same sentences synthesized. 1C:
same sentences synthesized and played backwards.
Cotton-top tamarins (n=13) were tested with the same
stimulus set as the newborns. Instead of sucking rate, how-
ever, we used a head orientation response toward the loud-
speaker. During the habituation phase, a tamarin was pre-
sented with sentences uttered by 2 speakers in one language
and then tested with a sentence uttered by a new speaker,
either in the same language (speaker change condition), or in
the other language (language change condition). Recovery
of orientation toward the loudspeaker was interpreted as an
indication that the tamarin perceived a difference between
the habituation and test stimuli (30).
Experiment 2A involved natural sentences of Dutch and
Japanese, played either forward or backward (31). Fig-
ure 2A shows that 10 out of 13 tamarins (p<0.05, bino-
mial test) dishabituated in the language change condition,
whereas only 5 out of 13 dishabituated to the speaker change
(p=0.87). The difference between language and speaker